MPEG-4 Profiles and Levels - A Practical Guide to Video and Audio Compression - page 673

Table G-5 Levels Versus Macroblocks (Continued)

Profile Level Max macroblocks Shape coding

Advanced Coding Efficiency 3 3240 √

Advanced Coding Efficiency 4 16320 √

N-Bit 2 792 √

Note:

Level-0 video must not exceed 176 horizontal or 144 vertical.

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These values are important because they must fit within buffer sizes agreed on by
the standards working group participants.

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Players' compliance with the standard requires that they have buffers of a particu-
lar size available.

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G.4 MPEG-4 Audio Object Types

The MPEG-4 audio specifications describe a range of different algorithms that can be used
to code the audio in the most appropriate and effective way. These are identified by short
mnemonic names and ID-values that are embedded in the content stream. The decoder
recognizes the algorithm that has been used to encode the audio and selects the correct
decoder for it.
Table G.6 lists a selection of the Audio Object Types (AOTs) that are currently defined.
Some of these are still under development and may not have been standardized yet.

Table G-6 Audio Object Types in MPEG-4

AOT Description ER

AAC main The main Advanced Audio Coding algorithm.

AAC LC Low complexity. √

AAC SSR Scalable Sampling Rate.

AAC LTP Long-Term Predictor. √

AAC SBR Spectral Brand Replication. Used in HE-AAC (AAC + ).

AAC Scalable Scalable coding. √

TwinVQ Transform-Domain Weighted Interleave Vector Quantization. √

CELP Code-Excited Linear Prediction. Used for speech coding. Also

available in an error-resilient form. √

Continued